Method of making a patch for a shrinkable bag

ABSTRACT

Disclosed is a protective patch for biaxially a heat shrinkable, thermoplastic vacuum bag for protecting the bag from puncture by sharp protruding bones in bone-in cuts of meat which are vacuum packaged within the bags. The patch is made from multi-layer film and preferably comprises outer layers of a blend of linear low density polyethylene and ethylene vinyl acetate copolymer and inner layers of ethylene vinyl acetate copolymer. The patch is heat shrinkable with the bag. A method of making the patch is also disclosed.

This is a continuation application of copending application Ser. No.035,836, filed on Apr. 8, 1987, now abandoned, which is a divisionalapplication of now abandoned application Ser. No. 740,360, filed on June3, 1985.

FIELD OF THE INVENTION

This invention relates to the packaging of bone-in cuts of meat. Inparticular, this invention relates to a protective patch which preventsor reduces the likelihood that a bone will completely puncture andrupture a thermoplastic vacuum bag and patch combination.

BACKGROUND OF THE INVENTION

The use of heat shrinkable thermoplastics as flexible packagingmaterials for vacuum packaging various foodstuffs including meat iswell-known. Such plastic materials, however, while in general quitesuccessful for packaging meat understandably have difficulties insuccessfully packaging sharp or bony products. For example, attempts topackage bone-in primal cuts of meat usually result in anunsatisfactorily large number of bag failures due to bone punctures. Theuse of cushioning materials such as paper, paper laminates, waximpregnated cloth, and various types of plastic inserts have proved tobe less than totally satisfactory in solving the problem. Thepreparation of special cuts of meat or close bone trim with removal ofoffending bones has also been attempted. However, this is at best only alimited solution to the problem since it does not offer the positiveprotection necessary for a wide variety of commercial bone-in types ofmeat. Furthermore, removal of the bone is a relatively expensive andtime consuming procedure.

Accordingly, it is one object of the present invention to provide apatch material and method for making the patch which will minimize andeliminate the puncturing of flexible, heat shrinkable vacuum bags bysharp bones.

An example of a prior art method of protecting a thermoplastic bag frompuncture is shown in U.S. Pat. No. 2,891,870 which issued on June 23,1959 to Meyer S. Selby et al. In the Selby patent the exposed bone in abone-in cut of meat is covered with a wax impregnated cloth and the thusprotected meat is placed in a heat shrinkable plastic bag. Accordingly,it is another object of the present invention to eliminate the necessityfor having a separate packaging item such as a wax impregnated clothwhich must be carefully positioned over the bone and provide aprotective patch which will not be as sensitive to or dependent upon theposition of the bone within a vacuum bag.

Another object of the present invention is to provide a patch for athermoplastic vacuum bag which is relatively strong and tough and whichcan be readily adhered to the outer surface of a thermoplastic vacuumbag.

These and other objects of the present invention will be more readilyunderstood from the summary of the invention, the drawings, and thedescription of the preferred embodiment which follow:

SUMMARY OF THE INVENTION

In one aspect, the subject invention is a method of making a multi-layerprotective patch for a heat shrinkable thermoplastic bag comprising thesteps of: coextruding a multi-layer thermoplastic tube, the inner wallof said tube comprising a first ethylene-vinyl acetate copolymer and theouter wall comprising a blend having a major proportion of linear lowdensity polyethylene and a minor amount of second ethylene-vinyl acetatecopolymer; applying a sufficient amount of powdered cornstarch or thelike to the interior of the tubular extrudate so that upon collapsing,the tube will not self adhere; collapsing the tube; irradiating thecollapsed tube to cross-link the materials thereof; opening, heating,and stretching the tube to biaxially orient the tube material;collapsing and flattening the oriented tube whereupon the tube adheresto itself; and cutting the tube into at least one patch.

In another aspect, the present invention is a protective, multi-layerpatch for a heat shrinkable vacuum bag comprising: an outer layercomprising a blend of 80% to 100% linear low density polyethylene, 20%to 0% ethylene-vinyl acetate copolymer having a vinyl acetate content inthe range of 7% to 12%, and 5% to 0% pigments and additives; an innerlayer comprising an ethylene vinyl acetate copolymer having 20% to 35%vinyl acetate content; and, said patch being biaxially heat shrinkable.In a particularly preferred embodiment the patch material has beencross-linked to the equivalent of a dosage level in the range between4.5 and 13 MR.

DESCRIPTION OF THE DRAWINGS

In the drawings which are appended hereto and made a part of thisdisclosure,

FIG. 1 is a perspective view of meat enclosed in a heat shrunk bag withthe patch of the present invention on the exterior thereof;

FIG. 2 is a perspective view similar to that in FIG. 1, but showing meatwith a prior art patch in position,

FIG. 3 is a sectional view taken along lines 3--3 of FIG. 1;

FIG. 4 is a fragmentary view showing the patch of the present inventionadhered to a thermoplastic vacuum bag;

FIG. 5 is a sectional view along lines 5--5 of FIG. 4; and

FIG. 6 is an exaggerated sectional view of the patch material of thepresent invention showing a preferred arrangement of the layers.

DETAILED DESCRIPTION

Referring more specifically to the drawings and to FIGS. 1-6, there isprovided a bone-in cut of meat 2, for example, a leg of lamb, havingexposed bone portion 6. There is also provided patch 8 on bag 12covering a substantial portion of the visible side of the package.Having the patch on the outside of the bag facilitates the step ofloading the bag by eliminating the concern over dislodging a manuallylaid on cloth patch or a patch adhered to the inside of the bag. Loadingcan, therefore, take place more readily and easily. After a bone-in cutis loaded into the bag air is evacuated from the package and the bagneck 10 is gathered having the appearance as shown in FIG. 1 andthereafter a clip 4 is applied to securely seal the bag. The bag canthen be immersed in hot water and shrunken tightly against the meat thusproviding a meat product in an evacuated atmosphere for aging andpreservation. The patch 8 shrinks with the bag thus reducing thetendency to delaminate when the patch is not shrinkable in the samemanner as the bag.

FIG. 2 shows a prior art bag 12 and covering cloth patch 8' whichrequires careful positioning of the cloth 8' over the bone 6 and alsorequires care in positioning the bone within the bag so that the cloth8' is not pushed out of position or dislodged.

FIG. 3 shows the exposed bone portion 6 covered by bag 12 with thepreferred patch 8 adhered to the outside of the bag over the boneprotrusion.

In FIG. 4 patch 8 is shown adhered to one side of a wall of bag 12.Preferably patch 8 will cover substantially one side of a bag in itsflattened, lay-flat position. In many applications it is desirable toadhere a patch to both sides of a bag.

FIG. 5 is a cross-section view of FIG. 4 showing patch 8 adhered to theone wall of bag 12.

FIG. 6 shows a cross-section, in an exaggerated form, of patch 8 withouter layers 14 and 16 and inner layers 18 and 20. In a preferredembodiment the composition of outer layers 14 and 16 comprises 87% byweight of linear low density polyethylene, 10% by weight ofethylene-vinyl acetate copolymer having 9% vinyl acetate and 3% pigmentsand additives to aid in extrusion. The preferred linear low densitypolyethylene is Dowlex 2045 from Dow Chemical Company of Midland, Mich.and the preferred ethylene-vinyl acetate copolymer is ELVAX 3128 fromthe DuPont Company of Wilmington, Del. The inner layers 18 and 20comprise ethylene-vinyl acetate copolymer having 28% vinyl acetate fromthe U.S.I. Division of National Distillers of New York, N.Y. All layershave been cross-linked by irradiation to the dosage level which isequivalent to 7 MR.

In one test bags were made with a 17.5 inches wide and 18 inches longpatch of the protective material of the present invention on one sideand a 17.5 inch wide and 10 inch long patch on the other. The lay flatdimensions of these bags were 18 inches wide by 30 inches long. In alarger bag (22"×34") for blades a patch of 21.5 inches by 24 inches onone side and a patch of 21.5 inches by 8 inches on the other was used.Various bone-in beef products were put up in bags with both the patch ofthe present invention as described and with cloth covered bones. Theproducts ranged from rib ends to blades and arms. Of the total of 1173packages which used cloth to cover the protruding bones there were atotal of 55 bone punctures whereas in 2097 packages using the patches ofthe present invention as described there were only 18 bone punctures.

The embodiment as described above is a preferred one but a satisfactorypouch can be made where the inner and outer layers 14 and 16 comprise15% ethylene-vinyl acetate copolymer having 9% vinyl acetate and 83.3%linear low density polyethylene with the balance of 1.7% being apigment. In addition, satisfactory pouches can be made with the outerlayers comprising a blend of 90% linear low density polyethylene with10% vinyl acetate copolymer. Based on experience it is believed that thedesirable composition range for the outer layer is 80% to 100% linearlow density polyethylene and 20% to 0% ethylene-vinyl acetate copolymerwith the vinyl acetate content having a range from 7% to 12% vinylacetate. The inner layer preferably comprises an ethylene-vinyl acetatecopolymer having 20 to 35% vinyl acetate content.

It has been surprisingly found that the increased strength and toughnessof the patch according to the present invention is greatly enhanced bythe use of linear low density polyethylene. The copolymers referred toas linear low density polyethylene generally have a density of 0.900 to0.935 grams per cubic centimeter and a crystalline melting point in therange of 110° C. to 125° C. These linear low density polyethylenes arenot homopolymers although they are referred to generally as"polyethylene". In fact, they are copolyers of ethylene and analpha-olefin having a carbon number less than 18, for instance,butene-1, pentene-1, hexene-1, octene-1, etc. In the Dowlex brand oflinear low density polyethylene used in the above preferred embodimentit is understood that the alpha-olefin is octene-1. Examples of patentsshowing the use of such polymers are U.S. Pat. No. 4,425,268 whichissued on Jan. 8, 1984 to Barry A. Cooper; U.S. Pat. No. 4,456,646 whichissued on June 26, 1984 to Nishimoto et al; U.S. Pat No. 4,399,180 whichissued on Aug. 16, 1983 to William F. Briggs et al; and U.S. Pat. No.4,457,960 which issued on July 3, 1984 to David L. Newsome.

Typical vacuum bags and the vacuum bag of the type used in the test andexample set forth above are made according to the process shown in U.S.Pat. No. 3,741,253 which issued on June 26, 1973 to Harri J. Brax et al.The method of the Brax et al patent is incorporated here in by referenceand provides background for the description which follows for the methodof making the patch of the present invention.

To make the patch of the present invention, a first ethylene-vinylacetate copolymer having a vinyl-acetate content of approximately 28% byweight is sent to a first extruder. This material forms layers 18 and20. (FIG. 6). Also, a blend having a major proportion of linear lowdensity polyethylene and a minor proportion of a second ethylene-vinylacetate copolymer, one having a vinyl acetate content in the range of 7%to 12%, is fed into a second extruder. This material forms layers 14 and16. Both extruders feed a common coextrusion die of the type which iswell-known in the art. The extrudate which issues from the die has aninner wall of the first ethylene-vinyl acetate copolymer and an outerwall of the blend. This type of coextrusion essentially coextrudes twoconcentric tubes, one inside the other, and in this case the first vinylacetate copolymer is the inner tube.

As the tube is extruded downwardly it is closed off and flattened bypinch rollers, but in order to keep the first vinyl acetate copolymerfrom adhering to itself the interior of the tube is coated with an inertdust or powder, preferably powdered cornstarch, in a surfaceconcentration sufficient to prevent self-adherence. This flattenedtubing is then fed through an irradiation vault where it will preferablyreceive a dosage of approximately 7 MR to cross-link the polymericmaterials which comprise the tube. The preferred range is 4.5 MR to 13MR with the most suitable range being between 6 and 8 MR. Chemicalcross-linking using an organic peroxide is thought to be an alternatecross-linking method but quite satisfactory results are obtained throughuse of irradiation cross-linking and irradiation cross-linking ispreferred. After receiving the cross-linking dosage the tube is opened,inflated, heated, and stretched by the well-known bubble technique whichis described in the above mentioned Brax et al patent. The biaxiallystretching orients the tube material. After the material has beenstretched to the desired diameter and wall thickness, it is thensimultaneously rapidly cooled and collapsed. This process results in abiaxially oriented patch material which is heat shrinkable atapproximately the temperature at which it was oriented. When collapsedand flattened the tubing will now tend to adhere to itself as thestretching decreases the concentration of the cornstarch on the innersurface of the bubble or stretched tubing. This concentration of thecornstarch now is low enough to permit self-adherence. The vinyl acetatecontent of the inner wall is approximately 28% by weight. This is anethylene-vinyl acetate copolymer in the range where the ethylene-vinylacetate copolymer acts as an adhesive. Thus, a multi-layer tubularmaterial is produced, in this instance, a four layer material as shownin FIG. 6 is produced. This material can be cut into patches and adheredto one or both sides of the heat shrinkable bag to produce a protectivematerial which will greatly diminish the occurrence of bone punctures.

Many suitable adhesives to adhere the patch to the bag are available andcan readily be selected by those skilled in the art, the tendency todelaminate having been greatly reduced as the patch shrinks biaxially asdoes the bag.

Having thus described my invention, I claim:
 1. A method of making amulti-layer protective patch for a biaxially heat shrinkablethermoplastic bag comprising the steps of:(a) coextruding a multi-layer,thermoplastic tube, the inner wall of said tube comprising a firstethylene vinyl acetate copolymer and the outer wall comprising a blendhaving a major proportion of linear low density polyethylene and a minoramount of a second ethylene vinyl acetate copolymer; (b) applying asufficient amount of an inert dust or powder to the interior tube wallso that upon collapsing, the tube will not self adhere; (c) collapsingthe tube; (d) irradiating the collapsed tube to cross-link the materialsthereof; (e) opening, inflating, heating, and stretching the tube tobiaxially orient the tube material; (f) simultaneously cooling,collapsing and flattening the tube whereupon the tube adheres to itself;and (g) cutting the tube into at least one patch.
 2. The method of claim1 including the additional step of adhering the patch to a surface ofthe shrinkable thermoplastic bag thereby protecting the bag frompuncture.
 3. The method of claim 1 wherein the vinyl acetate content ofthe second copolymer is in the range of 7% to 12% and the vinyl acetatecontent of the first copolymer is in the range of 20 to 35%, and whereinthe blend of linear low density polyethylene and the secondethylene-vinyl acetate copolymer comprises 80% to 100% linear lowdensity polyethylene, 20% to 0% ethylene-vinyl acetate copolymer, and upto 5% pigments and additives.
 4. The method of claim 3 wherein the tubeis irradiated in the dosage range of from 4.5 to 13.0 MR.
 5. A method ofmaking a multi-layer protective patch on a biaxially heat shrinkablethermoplastic bag comprising the steps of:(a) coextruding a multi-layer,thermoplastic tube, the inner wall of said tube comprising a firstethylene vinyl acetate copolymer and the outer wall comprising a blendhaving a major proportion of linear low density polyethylene and a minoramount of a second ethylene vinyl acetate copolymer; (b) applying asufficient amount of an inert dust or powder to the interior tube wallso that upon collapsing, the tube will not self adhere; (c) collapsingthe tube; (d) irradiating the collapsed tube to cross-link the materialsthereof; (e) opening, inflating, heating, and stretching the tube tobiaxially orient the tube material; (f) simultaneously cooling,collapsing and flattening the tube whereupon the tube adheres to itself;(g) cutting the tube into at least one patch, and (h) adhering the patchto a surface of the shrinkable thermoplastic bag thereby protecting thebag from puncture, wherein said patch will, when adhered to said bag,shrink with the bag, thereby reducing the tendency of the patch todelaminate from the bag.
 6. The method of claim 5, wherein the vinylacetate content of the second copolymer is in the range of 7% to 12% andthe vinyl acetate content of the first copolymer is in the range of 20to 35%, and wherein the blend of linear low density polyethylene and thesecond ethylene-vinyl acetate copolymer comprises 80% to 100% linear lowdensity polyethylene, 20% to 0% ethylene-vinyl acetate copolymer, and upto 5% pigments and additives.